radv: Update to new VK_EXT_vertex_attribute_divisor to version 2.
Behavior wrt firstInstance got changed, and a divisor of 0 has been
disallowed.
The new version of the ext got published in specification 1.1.81.
Sending to stable since the only known user is DXVK, which needs
this for correctness.
Reviewed-by:
Samuel Pitoiset <samuel.pitoiset@gmail.com>
CC: 18.2 <mesa-stable@lists.freedesktop.org>